1. Field of the Invention
This invention relates generally to solar powered pumping systems, and more particularly to a solar powered relatively balanced pumping system having a ground level electric driven pumping unit with counterbalance weights and a downhole pump with a return spring which provides a relatively balanced system between the total weight of the liquid column being lifted, the return spring torque, the counter balance weight, and a minimum powered DC motor to activate the pumping cycle.
2. Brief Description of the Prior Art
Conventional sucker rod pumping units have a gasoline motor driven "walking beam" which has a rotating flywheel and an oscillating arm having a curved head cable track at the outer end which moves up and down. A cable connected to the walking beam passes over the cable track and is connected at its lower end to a sucker rod. The sucker rod passes through a packer seal, down through the supply conduit and is connected at its lower end to a downhole pump which is disposed inside a well casing beneath the water table. The conventional sucker rod pump is a tubular member with a fixed "foot valve" (check valve) at the lower end. A piston is connected to the reciprocating sucker rod and travels up and down in the tubular pump housing and separates the housing into an upper chamber above the piston and a lower chamber below the piston. The piston also contains a check valve. On the up stroke of the sucker rod, the upper check valve in the piston closes and the lower check valve (foot valve) opens and water or oil is "sucked" up into the lower chamber of the pump housing. On the down stroke, the piston moves through the liquid in the lower chamber, the upper check valve in the piston opens and the lower check valve (foot valve) closes, and water or oil is now above the piston. On successive up strokes, the water is transported to the surface.
Solar powered pumping units are known wherein the gasoline engine is replaced by an electric motor coupled with photovoltaic cells for collecting electrical energy which is used to energize the above ground pumping unit or to power an electric downhole pump.
The up and down reciprocating motion of conventional pumping systems driven by solar, electric motor, or gasoline engine powered units requires the drive system to generate a given amount of torque force to activate the downhole pump. The depth of the well and the amount of head pressure as a result of the weight of the liquid column being pumped must be overcome by the force generated by the motor. The maximum amount of lift force required to be generated is on the up stroke and the minimum force is on the down stroke. Thus, the forces required to be overcome by the drive motor is not constant, but instead is unbalanced throughout each cycle. This unbalanced torque requirement labors the drive motor and results in shortened motor life. Starting the motor in an unbalanced or loaded condition will often result in motor stall or burn-out. Increasing the size or output of the motor increases power consumption and decreases operating efficiency.
Another problem with conventional downhole reciprocating pumps is that the pump piston is connected to the walking beam or fulcrum beam by a sucker rod which is coaxial with the discharge conduit and passes through a packer seal or stuffing box arrangement at ground level. This stuffing box seal is subject to leakage and failure and must be replaced often. The reciprocating motion of the sucker rod inside the discharge conduit can, through friction, rub against the conduit lining and cause eventual failure.
There are several patents which disclose various ground level pumping units and downhole pumps.
Slater, U.S. Pat. No. 4,586,879 discloses a solar powered rotary wheel pumping unit with cable connections through a system of pulleys to a conventional downhole reciprocating pump and has an adjustable stroke. The pump unit is described as operating in a conventional manner, thus a piston containing a check valve is connected to the lower end of the pump rod and on the up stroke of the pump rod, the valve in the piston closes and a lower check valve (foot valve) opens and liquid is sucked up into the pump housing. On the down or return stroke, the piston moves through the liquid in the housing. Slater provides a compression spring at the top end of the pump rod which is compressed when the pump rod moves upwardly (suction stroke) and aids in the down stroke of the pump rod (piston return through liquid) and also reduces shock on the pump rod and other components. The pump must rely on the total weight of the sucker rod created by gravity for the return of the piston to the beginning of the cycle. Slater provides spring assist on the unloaded down stroke, but makes no provision for balance between the loaded up stroke and the unloaded down stroke.
Allen, U.S. Pat. No. 4,681,515 discloses a solar powered walking beam pumping unit for use with downhole reciprocating pumps which has three motors and a self-adjusting counterweight which is extended inwardly or outwardly relative to one end of the walking beam by a rotating threaded shaft driven by one of the motors. There is also an element of inefficiency through the power consumption of the motors and a potential for failure where each is dependent upon the other.
McAnally, U.S. Pat. No. 4,744,334 discloses a solar powered oscillating pumpjack beam pumping unit and reservoir combination connected through a packer seal to a downhole reciprocating sucker rod pump. McAnally teaches a container at the outer end of the pumpjack beam into which counterweights may be added or removed to adjust pump efficiency, but offers no balance between the loaded up stroke and the unloaded down stroke. There is no provision other than gravity or shear motor torque for returning the sucker rod at the end of the lift cycle.
Gage, U.S. Pat. No. 2,238,692 and Meklensek, U.S. Pat. No. 1,053,525 discloses downhole reciprocating pumps driven by conventional electric motors which have a fixed check valve at the top of the barrel and a traveling check valve at the lower end which is reciprocated with lift rods exterior of the pump housing. There is no provision for solar power or balance between the loaded up stroke and the unloaded down stroke or for returning the sucker rod at the end of the lift cycle other than by gravity or shear motor torque.
The present invention is distinguished over the prior art in general, and these patents in particular by a solar powered pumping system having a ground level walking beam pumping unit and a downhole pump unit. The walking beam pumping unit has a solar powered electric motor which drives a flywheel through drive wheels and a centrifugal clutch to pivot a fulcrum beam having counterweights at one end. The other end of the fulcrum beam is connected by a lift wire to the downhole pump. The downhole pump has a pump housing with a stationary check valve at its upper end connected to a supply conduit extending to the surface. A traveling check valve/piston inside the pump housing is moved on the up stroke by a lift rod slidably mounted on the exterior of the housing which has a top end connected to the lift wire and a lower end connected to the traveling check valve/piston through a longitudinal slot in the lower housing. The traveling check valve/piston is returned on the down stroke by a tension return spring connected between the traveling check valve/piston and the pump housing. On the down stroke the traveling check valve opens and the stationary check valve at the top of the pump housing closes allowing liquid to enter. On the up stroke the traveling check valve closes, the stationary check valve opens, and the traveling check valve/piston lifts or pushes the liquid through the stationary check valve and subsequently to the surface. The return spring and counterweights produce a relatively balanced load condition to reduce power consumption and increase operating efficiency.